Using the Metabolic Chamber we have found a statistically significant increase in energy expenditure and respiratory quotient during 4 hours of hemodialysis compared to post dialysis levels; and a statistically significant increase in the 1st hour of hemodialysis compared to pre/post dialysis levels. The energy expenditure on non-dialysis days was lower compared to all values obtained on dialysis days. Results support the hypothesis that dialysis-related catabolism may contribute to the high incidence of malnutrition seen in HD patients.